TW201528748A - Method for determining search space - Google Patents

Abstract

A method for determining a search space of a physical downlink control channel in a wireless communication system, wherein the physical downlink control channel is periodically repeated in a time domain, the method characterized in that a starting position of the search space of the physical downlink control channel is unchanged within a repetition period of the physical downlink control channel.

Description

A method for determining a search space

The present invention relates to the field of communication technologies, and in particular to the field of wireless communication technologies.

In the field of wireless communication, in recent years, Machine Type Communication (MTC) is receiving continuous attention. Some MTC devices, typically such as smart instrumentation, need to be installed in the basement, so the penetration loss is so great that these devices may not be able to effectively connect to network devices. Therefore, 3GPP has set a subject specifically aimed at increasing the coverage of low-cost MTC devices. The goal is to increase the coverage of such MTC devices to 15dB.

In the existing 3GPP specifications, data transmission is scheduled based on a Physical Downlink Control Channel (PDCCH). In order to achieve a coverage gain of 15 dB on the MTC device, the corresponding PDCCH signal is expected to be transmitted repeatedly hundreds of times. Applying a higher aggregation level (Aggregation Level for short) can reduce the number of repetitions to a certain extent to save power consumption of the device. However, the implementation of coverage gain must depend on the PDCCH signal. Periodic repetition on the time domain.

In the current specification, the user equipment (User Equipment referred to as UE) including the MTC device blindly decodes all possible PDCCH channel signals in one subframe to find the PDCCH channel for scheduling itself. The position and number of Control Channel Elements (CCEs) occupied by each PDCCH channel are changed in each subframe to avoid continuous congestion. For the same reason, the search space of each PDCCH channel is also changed in units of subframes. This change is achieved by some kind of hash function, providing some degree of randomness to avoid continuous congestion.

It is not difficult to see that there is a contradiction between the existing search space mechanism and the periodic repetition of the PDCCH signal in the time domain. When the PDCCH signal needs to be repeated on hundreds of subframes, and the search space of each subframe is different, the above MTC device must blindly decode all possible subframes on all subframes in the repetition period. The PDCCH channel finds the PDCCH channel that repeats but the search space has been changing. Obviously, this greatly increases the complexity of the implementation of the MTC device; it is inconsistent with the low-cost, easy-to-implement design concept of the MTC device itself.

Therefore, the object of the present invention is to find a new method for determining the PDCCH channel search space; this method needs to be applicable to the case where the PDCCH signal is periodically repeated in the time domain to achieve the coverage gain of the MTC device; Complex, so as not to increase the cost of MTC equipment; at the same time, it should be compatible with existing specifications as much as possible to avoid There are agreements that have changed too much.

To solve the above problems in the prior art, the present invention proposes a novel method for determining a PDCCH channel search space. By transforming the search space based on the subframe change into the search space based on the repetition period change, the periodic repetition of the PDCCH signal in the time domain is realized in a simple manner, thereby solving the above problems existing in the existing specifications.

Specifically, according to a first aspect of the present invention, a method for determining a search space of a physical downlink control channel in a wireless communication system is provided, wherein the physical downlink control channel is periodically repeated in a time domain, and the method thereof The feature is that the starting position of the search space of the physical downlink control channel does not change during the repetition period of the physical downlink control channel.

Preferably, a start function of the search space of the physical downlink control channel is determined using a hash function associated with a repetition period of the physical downlink control channel.

More preferably, the starting position of the search space of the physical downlink control channel is determined using the following formula:

Where L represents the aggregation level; Yj represents the hash function associated with the repetition period of the physical downlink control channel; m =0, . . . , M-1, M represents the number of possible physical downlink control channels N _CCE,k represents the total number of control channel elements in subframe k , i =0,..., L -1.

More preferably, the hash function Yj related to the repetition period of the physical downlink control channel is: Y _j = ( A . Y _{j -1} ) mod D

Where Y-1 = n _RNTI , n _RNTI represents the temporary identifier of the wireless network; A = 39827; D = 65537; j is determined by the following formula:

Wherein, SFN represents a system frame number; R represents a repetition period of the physical downlink control channel; , ns represents the slot number in the radio frame.

More preferably, the hash function Yj related to the repetition period of the physical downlink control channel is: Y _j = ( A . Y _{j -1} ) mod D

Where Y-1 = n _RNTI , n _RNTI represents the temporary identifier of the wireless network; A = 39827; D = 65537; j is determined by the following formula:

Wherein, SFN represents a system frame number; R represents a repetition period of the physical downlink control channel; , ns represents the slot number in the radio frame; k2 _i is determined by the following formula: (10* SFN _i + n _i + k1 _i ) MOD( R + k2 _i )=0

The SFN _i represents the system frame number of the repetition period of the ith physical downlink control channel; n _i represents the initial subframe number in the repetition period of the i th physical downlink control channel; R represents The repetition period of the physical downlink control channel, k1 _i and k2 _i represent the offset associated with n _i .

More preferably, physical resources are reserved for the common search space.

More preferably, the starting position of the search space of the physical downlink control channel is determined using the following formula:

Where L represents the aggregation level; Yj represents the hash function associated with the repetition period of the physical downlink control channel; m =0, . . . , M-1, M represents the number of possible physical downlink control channels , N _CCE,k represents the total number of control channel units in the subframe k ; n _{CCE, CSS} represents the control channel unit reserved for the common search space, i =0,..., L -1.

Preferably, multiple aggregation levels can be configured during the repetition period of the physical downlink control channel.

More preferably, a plurality of the search spaces may be configured during a repetition period of the physical downlink control channel.

More preferably, the control channel units constituting the search space are non-continuously distributed, characterized in that the distribution of the control unit does not change within a repetition period of the physical downlink control channel.

In the present invention, by designing a new function, the search space is changed to change based on the repetition period, thereby realizing that the search space remains unchanged in one repetition period, so that the implementation of the blind decoding operation of the MTC device is greatly simplified; at the same time, the search space is ensured. Different recurring periods are different, thus avoiding the occurrence of persistent congestion; in a preferred solution, resources of the common search space can also be reserved to achieve flexible scheduling, and other The type of user equipment is affected; and the existing specifications are compatible to the greatest extent, and excessive modifications to the agreement are avoided, thereby achieving the object of the present invention.

Other features, objects, and advantages of the present invention will become apparent from the Detailed Description of Description

1 shows a flow chart of a method of determining a PDCCH channel search space in accordance with the present invention.

Wherein, the same or similar reference numerals indicate the same or similar step features or devices/modules.

In the detailed description of the preferred embodiments that follow, reference is made to the accompanying drawings that form a part of the invention. The accompanying drawings illustrate the specific embodiments of the embodiments of the invention. The exemplary embodiments are not intended to be exhaustive of all embodiments in accordance with the invention. It is to be understood that other embodiments may be utilized and structural or logical modifications may be made without departing from the scope of the invention. Therefore, the following detailed description is not to be construed as limiting the scope of the invention.

First, in the existing 3GPP specifications, the search space of the PDCCH channel is defined by the following formula:

Where L represents the aggregation level AL; Yk represents a hash function; m =0,..., M-1, and M represents the number of possible PDCCH channels; N _CCE,k represents the content contained in the subframe k The total number of CCEs, i =0,..., L-1. The hash function represented by Yk is defined in the existing specification as follows: Y _k = ( A . Y _{k -1} ) mod D (2)

Wherein, Y-1 = n _RNTI , n _RNTI represents a radio network temporary identifier (RNTI); A = 39827; D = 65539; , ns represents the slot number in the radio frame. It can be seen from the formula (2) that the hash function Yk used in the specification is changed based on the subframe, that is, the starting CCE positions of the search spaces of the same PDCCH channel are different on each different subframe. .

Therefore, according to the present invention, a modification of the PDCCH channel search space is proposed, that is, when a certain PDCCH channel is periodically repeated in the time domain, the PDCCH channel is used in each subframe in a repetition period of the PDCCH channel. The starting CCE position of the search space is constant.

1 is a flow chart showing a method for determining a PDCCH channel search space according to the present invention, including the following steps:

S11. The start position of the search space of the physical downlink control channel does not change during the repetition period of the physical downlink control channel.

Specifically, according to an embodiment of the present invention, it is proposed to replace the subframe-based hash function Yk with a hash function Yj based on a PDCCH channel repetition period. The purpose of using Yj is to ensure that the search space is constant during the repetition period, and to achieve a certain degree of random distribution between repetition periods, thereby reducing the probability of congestion occurring. In this way, the new search space can be expressed as:

Wherein, L represents AL; Yj represents the hash function associated with the repetition period of the physical downlink control channel; m =0, . . . , M-1, M represents the number of possible PDCCH channels; N _CCE,k Represents the total number of control channel elements in sub-frame k , i =0,..., L -1. It must be pointed out that formula (3) is only one implementation of the method for determining the search space according to the present invention, and any other formula that uses the hash function based on the repetition period to determine the search space can achieve the same effect, and thus belongs to the present invention. protected range.

Further, according to another embodiment of the present invention, Yj in the formula (3) can be expressed as: Y _j = ( A . Y _{j -1} ) mod D (4)

Where Y-1 = n _RNTI ; A = 39827; D = 65537; j is determined by the following formula:

Wherein, SFN represents a system frame number; R represents a repetition period of the PDCCH channel; , ns represents the slot number in the radio frame. From equation (5) can be seen, the introduction of a repetition period R, thus within each repetition period R, the starting position of the search space on the CCE of the respective subframes are the same; in different repetition period R The starting CCE positions of the search space are different. For example, when R =50, the starting CCE positions of the PDCCH channel search space are the same in the first 50 subframes, and the 51st subframe, the starting CCE location of the PDCCH channel search space occurs. Change, and then keep the next starting CCE position until the 100th subframe, and so on.

More preferably, in order to further reduce the probability of congestion, according to another embodiment of the present invention, the hash function used may be changed at the end of each repetition period, that is, different hash functions are used in each repetition period to determine the search. Space, and all these hash functions are based on repeating cycles. The following formula gives a formula based on the hash function of this embodiment: Y _j = ( A . Y _{j -1} ) mod D (4-1)

Where Y-1 = n _RNTI , n _RNTI represents the temporary identifier of the wireless network; A = 39827; D = 65537; j is determined by the following formula:

Wherein, SFN represents a system frame number; R represents a repetition period of the physical downlink control channel; , ns represents the slot number in the radio frame; k2 _i is determined by the following formula: (10* SFN _i + n _i + k1 _i ) MOD( R + k2 _i )=0 (6)

The SFN _i represents the system frame number of the repetition period of the ith physical downlink control channel; n _i represents the initial subframe number in the repetition period of the i th physical downlink control channel; R represents The repetition period of the physical downlink control channel, k1 _i and k2 _i represent the offset associated with n _i . It can be seen from the formula (6) that since the offset k2 _{i is} introduced, the parameter j obtained by the formula (5-1) is different in each repetition period R , so that each repetition period R is The formula (4-1) used also becomes different. This achieves higher randomness and can effectively prevent congestion.

In addition, considering that the repeated transmission of the PDCCH is bound to occupy a large amount of channel resources, it will inevitably increase the congestion degree of the system. In an extreme case, it may even affect the common search space of the common control channel (Common Search Space for short). . As we all know, CSS is an important system resource, and we must try to reduce the impact of PDCCH repetition. Therefore, according to another embodiment of the present invention, a method for determining a PDCCH channel search space by using a repetition period-based hash function is proposed, and a physical resource is reserved for a CSS, so that a resource used by the CSS is not repeatedly transmitted by the PDCCH. Occupied, thus avoiding the impact of repeated transmission of PDCCH on CSS.

Further, according to another embodiment of the present invention, the search space can be expressed as:

Where L represents AL; Yj represents a hash function related to the repetition period of the PDCCH; m =0, . . . , M-1, M represents the number of possible physical downlink control channels, N _{CCE, k} represents a sub-signal The total number of CCEs in block k ; n _{CCE, CSS} represents the CCE reserved for CSS, i =0,..., L -1. Obviously, any other formula that uses a repeating cycle-based hash function and reserves the physical resources for the CSS can achieve the same effect, and thus belongs to the protection scope of the present invention.

In addition, in order to meet the needs of flexible scheduling, according to another embodiment of the present invention, a plurality of different repetition periods may be configured on one MTC device, or multiple ALs may be configured on one repetition period, in this case, The MTC device needs to perform a blind decoding operation on the multiple repetition periods to obtain a corresponding PDCCH signal.

In order to improve the efficiency of using channel resources, according to another embodiment of the present invention, multiple search spaces may be configured on one repetition period. For example, all the sub-frames in a repetition period can be divided into two groups according to the parity of the sub-frame number, each group is used for different search spaces, and the MTC device correspondingly receives the received signal according to the sub-frame number. The parity is combined separately and blindly decoded to obtain the corresponding PDCCH signal.

Finally, in order to further reduce the probability of occurrence of congestion, according to another embodiment of the present invention, the CCEs constituting the search space may be discontinuously distributed as long as the distribution of these CCEs is kept constant within the repetition period R of the PDCCH. For example, when AL=8, the search space occupies 8 CCEs, and the 8 CCEs may be logically non-continuously distributed, for example, two groups of 4 CCEs, with 4 intervals between the two groups. CCE. The method of the present invention is equally applicable as long as it is guaranteed that the eight CCEs on each subframe are distributed in the same repetition period R.

The embodiments of the present invention have been described above, but the present invention is not limited to the specific systems, equipment, and specific protocols, and various modifications and changes can be made by those skilled in the art within the scope of the appended claims.

Those of ordinary skill in the art can explain through research Other variations to the disclosed embodiments are understood and effected by the appended claims. The word "comprising" does not exclude other elements and steps, and the word "a" does not exclude the plural. In the present invention, "first" and "second" refer only to names, and do not represent order relationships. In the practical application of the invention, a part may perform the functions of a plurality of technical features cited in the scope of the patent application. Any reference signs in the claims should not be construed as limiting the scope.

Claims (10)

A method for determining a search space of a physical downlink control channel in a wireless communication system, wherein the physical downlink control channel is periodically repeated in a time domain, the method is characterized in that, in a repetition period of the physical downlink control channel, the The starting position of the search space of the physical downlink control channel does not change. The method of claim 1, wherein the starting position of the search space of the physical downlink control channel is determined using a hash function associated with a repetition period of the physical downlink control channel. The method of claim 2, wherein the starting position of the search space of the physical downlink control channel is determined using the following formula: Wherein L represents aggregation level; Yj associated with the repetition period representative of the physical downlink control channel of the hash function; m = 0, ..., M -1, M represents the possible number of the physical downlink control channel; N _CCE,k represents the total number of control channel elements in subframe k , i =0,..., L -1. The method of claim 3, wherein the hash function Yj associated with a repetition period of the physical downlink control channel is: Y _j = ( A . Y _{j -1} ) mod D where Y-1 =n _RNTI , n _RNTI stands for wireless network temporary identification; A =39827; D =65537; j is determined by the following formula: Wherein, SFN represents a system frame number; R represents a repetition period of the physical downlink control channel; , ns represents the slot number in the radio frame. The method of claim 3, wherein the hash function Yj associated with a repetition period of the physical downlink control channel is: Y _j = ( A . Y _{j -1} ) mod D where Y-1 =n _RNTI , n _RNTI stands for wireless network temporary identification; A =39827; D =65537; j is determined by the following formula: Wherein, SFN represents a system frame number; R represents a repetition period of the physical downlink control channel; , ns represents the slot number in the radio frame; k2 _i is determined by the following formula: (10* SFN _i + n _i + k1 _i ) MOD( R + k2 _i ) = 0 where SFN _i represents the i-th physical The system frame number of the repetition period of the downlink control channel; n _i represents the initial subframe number in the repetition period of the i-th physical downlink control channel; R represents the repetition period of the physical downlink control channel, k1 _i and k2 _i represents the offset associated with n _i . The method of claim 2, wherein the physical resource is reserved for the common search space. The method of claim 6, wherein the starting position of the search space of the physical downlink control channel is determined using the following formula: Where L represents the aggregation level; Yj represents the hash function associated with the repetition period of the physical downlink control channel; m =0, ..., M-1, M represents the number of possible physical downlink control channels, N _CCE,k represents the total number of control channel units in the subframe k ; n _{CCE, CSS} represents the control channel unit reserved for the common search space, i =0,..., L -1. The method of claim 1, wherein a plurality of aggregation levels are configurable during a repetition period of the physical downlink control channel. The method of claim 1, wherein a plurality of the search spaces can be configured during a repetition period of the physical downlink control channel. The method of claim 1, wherein the control channel units constituting the search space are non-continuously distributed, wherein the distribution of the control unit is constant within a repetition period of the physical downlink control channel.